In EDM (electric discharge machining) technology, various pulse generators are used depending on the task at hand. For EDM cutting, deionized water is primary used as dielectric because of its good properties, in particular in view of the good material removal properties as to the workpiece. For the attainment of maximum material removal, the pulse generator must have certain properties.
Known pulse generators exhibit, when deionized water is used as the dielectric in the working gap, the disadvantage that the potential maximum material removal per unit of discharge energy cannot be attained because the duration of the pulse cannot be made substantially shorter than 1 microsecond, and the decay curve of the current pulse cannot be made sufficiently steep. This is due to the fact that the electrical output elements used in the principal circuit of the pulse generator for current limitation and current control cannot follow the requisite short pulse duration and steep decay curve.
A pulse generator for wire EDM which can furnish short pulses of one microsecond and high currents of several hundred amperes is described in German patent No. 2,735,403. A further shortening of the pulses and a further increase in the steepness of the decay curve is not possible resistances because of the stray inductivity of the output. Furthermore, this pulse generator exhibits, because of the output resistance, an economically unacceptable loss of efficiency.
To avoid these disadvantages, a pulse generator is described in the European Pat. No. 160,989 which has a good efficiency, because it exhibits inductivity in the principal circuit in place of the output resistance. For this reason, neither the desired short pulse duration nor the steep decay curve can be improved with this generator to the extent that the pulse duration lies at 0.1 microsecond and the decay curve of the current pulses lies at over 1000 amperes per microsecond. This derives from the fact that the working current must flow via at least five switching elements.